This invention relates to track alignment devices and, more particularly, to track alignment devices utilising a "chord system" to obtain track alignment error and correct track alignment.
It has previously been proposed in Russian Pat. No. 471,413 which was granted on May 25, 1975 to Turovskiy et al, to use a wire stretched between forward and rearward stations of a track alignment device, the wire serving as a chord of a curved section of the track over which the alignment device is passing to establish a datum or reference line. A first measuring device located relatively near the forward station cooperates with the wire to measure the distance of the track at successive points from the reference line. A predetermined number of measurements are obtained and averaged. A second measuring device located relatively near the rearward station cooperates with the wire to measure successively the distance from the reference line of the track at a point immediately forwardly of the already corrected track portion. The actual value obtained is compared with the mean value obtained from the first measuring device and an error signal generated if there is a difference. The error signal causes an alignment mechanism to shift the track in a direction left or right and by an amount to remove or reduce the error.
This prior system suffers from the disadvantage that the length of the chord is limited physically by the practical problems associated with supporting the wire on rail cars. This places a practical limitation on the precision of the measurements because the longer the chord the more precise the measurements.
Another disadvantage of the prior system is that because the first measuring device is located near the forward end of the wire then, if the forward end of the wire is on a badly misaligned point on the track, a large deviation from a "true" displacement from the reference will be present in the reading obtained.